Most monoclonal antibodies and antisera to human and animal viruses are derived from conventional in vivo immunization using whole virus, isolated envelope protein components, or synthetic peptides derived from proteins exposed on the virus exterior. Thus, these reagents are uniformly directed against external viral components. The usefulness of such antibodies for diagnostic purposes is limited by the poor cross reactivity among even closely related viruses, a consequence of the extensive genetic drift affecting the amino acid sequences of externally oriented viral proteins. Due to this poor cross reactivity these anti-viral antibodies are not useful for routine screening and diagnoses--antibodies produced against one isolate of a genetically variable virus (such as HIV or influenza) will often fail to react with the virus infecting a second set of patients. Also, typical diagnostic tests which detect viral infections measure the level of circulating anti-viral antibodies in a patient's serum and do not directly measure the presence of the virus. Therefore, a need exists for a method to directly identify related but serologically distinct viruses.